Plants processing foods, pharmaceuticals, biological and technological fluid materials generally require fluid piping systems that must be free from voids and crevices to prevent accumulations of materials, that can readily be taken apart for periodic cleaning and that can withstand the application of CIP (clean in place) solutions and steam cycles used for cleaning. The gasket material used at joints in the piping systems must have appropriate resiliency and resistance against deterioration by the chemical and physical characteristics of the fluids under the conditions of temperature and pressure occurring during santization, such as the use of 15 psi saturated steam, hot, de-ionized water or hot WFI (water for injection).
As compared to a general use gasket, the material for a sanitary-pipe gasket to be used in manufacturing medicines, foods, etc. must be more carefully selected. This requirement is made to prevent contamination of products by components of the gasket material eluting into the fluid transported through the piping. Accordingly, many sanitary-pipe gaskets have conventionally been formed of silicone rubber which has excellent heat resistance and chemical resistance. Other materials employed in food and pharmacological processing include ethylene propylene diene monomer (EPBM), buna rubber, and fluoroelastomers such as Viton® or FKM 615A™ a dipolymer of vinylidene fluoride and hexafluoroproplyene often used as base elastomers for seals, spacers and gaskets employed in sanitary piping systems
In addition to gaskets, elastomeric materials in various configurations are used in the food and pharmacological processing industries. For example, U.S. Pat. No. 2,985,470 illustrates the use of conical gaskets machined from polymeric tetrafluoroethelene. U.S. Pat. No. 4,531,532 illustrates the use of elastomeric materials in valve stems, seats and seals employed in sanitary fittings. Assembly and disassembly of sanitary pipe sections is facilitated by using flanged pipe ends held together by hinged clamps rather than by threaded coupling, as shown in U.S. Pat. No. 4,568,115. Gaskets in the form of O-rings for sealing the flanged ends of sanitary piping against leakage are shown in U.S. Pat. Nos. 5,904,382 and 5,971,399.
The '382 patent noted that the gasket shown in the '470 patent was subject to being objectionably deformed when clamped between opposed ends of the pipes of a pipe fitting so that it became unusable after several uses. In an attempt to make the gasket re-usable, the '399 patent resorted to a gasket made of porous, composite materials having different densities and which were differently compressible, so as to offer both effective sealing as well as resistance to cold flow.
In my recent U.S. Pat. No. 6,857,638 issued Feb. 22, 2005 I disclose a gasket for establishing a seal between the flanges of sanitary pipe fittings which comprises an O-ring portion of elastomeric material and an incompressible ring member bonded to the O-ring portion to limit compression of the elastomeric material so that it is prevented from intruding into the lumen of the pipe when the fitting is made up. This feature is achieved by dimensioning the axial thickness of the incompressible portion with respect to the axial thickness and percentage radial expansion of the elastomeric portion so as to limit its axial compression to an amount that takes into account the fact that its percentage radial expansion is greater than its percentage of axial compression by the factor (1/(1−t/T), where t is the amount of compression and T is the uncompressed axial thickness.
The foregoing patents have been concerned with maintaining an appropriate seal at the joints between piping sections to guard against the introduction of contaminants as well as the accumulation of processed materials at the gasketed joints. In addition, current standards of practice dictate that product purity be monitored to detect the presence of foreign matter in the process stream such as extraneous metals arising from broken machinery or processing equipment components. As expressed in the Federal Register (Vol. 51, No. 118): “Effective measures shall be taken to protect against the inclusion of metal or other extraneous material in food. Compliance with this requirement may be accomplished by using sieves, traps, electric metal detectors or suitable means.”
A common form of metal detector uses a balanced three-coil arrangement which is positioned to surround a section of pipe to sense metal moving through it. The center (oscillator) coil emits an electromagnetic field throughout the space within the metal detector housing. Two receiver coils (placed equidistant on either side of the oscillator coil) are connected in series so that the energy coupled from the oscillator coil to either of the receiver coils exactly cancels the energy coupled to the other receiver coil; the net output of this pair is essentially zero. Metal passing through this set of coils creates an imbalance which can be detected. For example, one standard of metal detector sensitivity is the ability to detect a metallic ball 1.5 mm in diameter mixed in with the process stream of normally product.
However, while such metal detectors may be able to detect the presence of ferrous and non-ferrous metals, other foreign matter, such as pieces of plastic or rubber will pass through undetected. One source of such foreign matter may be attributed to the wear and tear of the non-ferrous elastomeric materials used in gaskets, coated valve stems and seals exposed to the process stream but which also must withstand the high temperature steam periodically used to clean the piping systems. To detect such non-magnetic materials in the process stream expensive x-ray detection or gamma ray spectrometry apparatus has heretofore been required. X-ray systems can reliably detect metal, bone, grit, glass and some plastics (if thick enough).